Mack announcing Senate bid Friday

A release is billing the 10 a.m. rollout at the county courthouse in Ft. Myers as a "major announcement regarding the 2012 race . . . against liberal incumbent Bill Nelson."

Mack will be the third official Republican to enter the campaign, following former Col. Mike McCalister and Senate President Mike Haridopolos.

The fourth-term Republican has been making the moves towards a run for months now, writing op-eds chastising the two-term Democratic incumbent and frequently using him as a punching bag in his fundraising appeals.

In January, Mack asked supporters to help him raise money to get him ready for "the next opportunity."

Mack's advisers had privately calculated that the congressman could wait the longest of all the possible contenders to dive into the race because of the lasting name recognition established by his father.

But this earlier than expected vault into the fray could be seen as a reaction to the likelihood of a crowded field and recent stumbles by Haridopolos.

Mack, though, will likely have to confront questions from conservatives about his own stand on illegal immigration. This past summer he urged state lawmakers against pursuing an immigration law like Arizona's, which he compared to Nazi Germany.

Former Sen. George LeMieux and former House Majority Leader Adam Hasner are also expected to formalize their candidacies in the coming weeks.